Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.56   6.615%   $263.9361   $263.94   $263.95   $263.90  
  Purchase #2 $156.97   13.388%   $177.9851   $177.99   $178.00   $178.00  
  Purchase #3 $236.96   11.316%   $263.7744   $263.77   $263.75   $263.80  
  Purchase #4 $222.73   11.292%   $247.8807   $247.88   $247.90   $247.90  
  Purchase #5 $16.66   4.150%   $17.3514   $17.35   $17.35   $17.40  
  Purchase #6 $162.76   10.427%   $179.731   $179.73   $179.75   $179.70  
  Purchase #7 $151.72   7.501%   $163.1005   $163.10   $163.10   $163.10  
  7 purchase totals = $1,195.36       $1,313.7592   $1,313.76   $1,313.80   $1,313.80